In multihop wireless networks, selfish nodes do not relay other nodes' packets and make use of the cooperative nodes to relay their packets, which has negative impact on the network fairness and performance. Incentive protocols use credits to stimulate the selfish nodes' cooperation, but the existing protocols usually rely on the heavyweight public-key operations to secure the payment. In this paper, we propose secure cooperation incentive protocol that uses the public-key operations only for the first packet in a series and uses the lightweight hashing operations in the next packets, so that the overhead of the packet series converges to that of the hashing operations. Hash chains and keyed hash values are used to achieve payment nonrepudiation and thwart free riding attacks. Security analysis and performance evaluation demonstrate that the proposed protocol is secure and the overhead is incomparable to the public-key-based incentive protocols because the efficient hashing operations dominate the nodes' operations. Moreover, the average packet overhead is less than those of the public-key-based protocols with very high probability due to truncating the keyed hash values.